Depending on your location in the country or world, many types of food could already be available in your surroundings depending on the time of the year.
Since the purpose of this book is self reliance lets operate with the idea of having a permanent connection to your land and surrounding area. As you look at the location you are living in. You need to keep your eyes open on a weekly basis. New types of fruit and vegetable can make themselves available to you as the seasons progress. Marking on a calendar when and where you harvested will keep you prepared for next year.
You must avoid the tendancy to over exploit any one food. This leads to stomach upset very quickly and a poor diet will create health issues as time progresses. Their have been times when I paid the price for too many green apples or too much yellow wood sorrel.
The list of edibles is incredibly long: Yellow Wood Sorrel, Apples and Crab apples, blackberries, raspberries, blueberries, strawberries, wild carrots, grapes, and currants are just some of my favorites from my area. Other areas that I have been in offer; coconuts, mango, banana, paw paw, bamboo and sea weed. Exploration of your area is the only way to get a full knowledge of what is available to you.
Even the smallest amount of care for these wild plants will pay you back with large dividends. Remove weeds from around the plants, make sure they get some water in a dry spell and pruning fruiting trees as needed are all quick easy methods of improving your harvest.